There is a need during some medical procedures, such as in electrophysiology studies, to process images and cardiac electrical signals in synchronization with the respiration of a patient or to selectively base certain processes on the instantaneous phase of the respiration cycle. In electrophysiology, for example, the important issue is the motion of the heart and catheters within the heart which result from respiration and not the actual perfusion of air into the lungs. In such cases, the motion of the diaphragm or lungs or other respiration-driven movement may be of more interest than actual oxygenation of blood, and so estimation of respiratory phase is more particularly directed at tracking the motion of the diaphragm which may occur during respiration or during obstructed apnea or even perhaps during artificial ventilation.
Other methods exist in the art for estimating respiratory phase from fluoroscopic images. For example, U.S. patent application Ser. No. 15/487,245 titled “Rapid 3D Cardiac Parameter Mapping” (Sra et al.), filed on Apr. 13, 2017, discloses a method which estimates respiratory phase by analyzing the motion of an identified cardiac sensor, such as a catheter, placed in the heart. Such method determines the respiratory phase of an image from changes from frame-to-frame in a single coordinate of the positions of the identified sensor.
There is a need for a method which takes advantage of the larger amount of data in an image which contains some information about respiratory phase. When portions of a fluoroscopic image larger than individual objects such as a catheter include anatomic structures such as the diaphragm, ribs or lung which undergo displacement within the image due to respiration, such portions of the image can provide a more reliable indication of respiratory phase than the local motion of an object such as a catheter.